Dish-type antennae or antennas are widely used to receive signals from satellites. These dish antennas are usually about ten feet in diameter, and concentrate the received signal at the focal point of the dish, where the high frequency electromagnetic radiation is detected, amplified, and converted to a lower frequency for ease in transmission over coaxial cable to the television user's home.
In the past, most satellite transmissions were at C-band, having a frequency band of about 3.7.times.10.sup.9 to 4.2.times.10.sup.9 Hertz, or cycles per second. This is about 4 billion cycles per second, and, with the speed of light being about 3.times.10.sup.10 centimeters, or roughly three inches. This figure of three inches for the wavelength is significant, because antenna and associated electromagnetic waveguiding and wave handling structures must be physically matched to the length of the electromagnetic waves being handled.
More recently, certain satellites have also been transmitting at KU-band, at a frequency of about 11.7.times.10.sup.9 to 12.2.times.10.sup.9 Hertz. This corresponds to a wavelength of about one inch.
It would naturally be desirable to pick up both C-band and KU-band signals with a single dish installation. However, the different geometries required for handling the three inch electromagnetic waves and the one inch electromagnetic waves at the focus of a dish have caused significant difficulties in receiving and processing both frequency bands.
One initial attempt involved using the two necessary receiving assemblies, and placing them side by side each slightly away from the focal point of the dish antenna. However, the signals from the distant satellites are so weak, that the further degradation caused by this arrangement made it unsatisfactory.
Another attempted solution to the problem was to have a central small KU-band pick-up matched to the one inch wavelength, and two mutually orthogonal C-band pick-up members mounted around the KU-band assembly. In addition, two amplifier/converters were used, one for each of the C-band pick-ups. This arrangement was expensive as requiring the two amplifier/converters, and created an unwieldy, heavy, and out-of-balance assembly at the focal point of the dish.
Additional co-boresight attempts have proposed using a central small KU-band pick-up, and four peripheral C-band pick-up elements which transmit, via four waveguide or coaxial lines to an adjacent zone where four additional radiation elements re-generate the incoming C-band signal for pick-up by a single C-band antenna element. However, these proposed arrangements are relatively heavy, and introduce noise and loss as a result of passing through the transmission lines and two sets of antenna elements.
As noted hereinabove, prior proposals for providing a single installation to handle both C-band and KU-band have not been satisfactory; and accordingly, an important object of the present invention is to provide a new C-band and KU band configuration which provides optimum reception for signals of both bands, and which is not subject to the disadvantages of prior proposed arrangements, as discussed above.
It is further noted that, in converting from a system which handles only C-band signals to a system which handles both C-band and KU-band, the customer has had to throw away some of his C-band equipment, rather than merely purchasing new KU-band equipment to supplement his C-band equipment.
Accordingly, another object of the present invention is to provide a high quality compatible system wherein an initial C-band installation may be up-graded by the addition of KU-band equipment without the need for discarding any of the prior installation, and with minimal installation changes.